The field of the invention is polyamide compositions containing particulate metal fillers and the invention is particularly concerned with the application of these compositions to injection molded practice hand grenades and shells.
The state of the art of producing polyamide compositions containing fillers and processing these compositions by injection molding may be ascertained by reference to the Kirk-Othmer, "Encyclopedia of Chemical Technology", 2nd Edition, Vol. 16 (1968) under the section "Polyamides (Plastics)," pages 88-105, particularly page 92--polylauryllactam (nylon-12), pages 98-99--injection molding and extrusion and pages 101-102--Powder Processing, the disclosures of which are incorporated herein along with U.S. Pat. No. 3,317,482 which shows the state of the art of polylauryllactam production.
The state of the art of practice hand grenades and shells comprising metal powder filled compositions may be ascertained by reference to U.S. Pat. Nos. 3,194,161; 3,369,486 and 3,463,047 the disclosures of which are incorporated herein.
According to the present invention a molding composition is provided which is densely filled with fine particulate metals and which can be worked into molded articles by injection molding. Such molded articles should be dimensionally stable under ordinary conditions, that is, they should not break, for instance when being dropped, while on the other hand they should disintegrate when subjected to a high force, for instance to an explosive, into the finest possible particles which practically can no longer be located a few meters from the disintegration site. In particular the molding composition should be practical in the preparation of training hand grenades or mortar shells. For those applications, the molded article must be of a weight corresponding to that of a well defined grenade or shell.
It is known to arrange the effectively disintegrating metal particles inside such ammunition in a thermoplastic such as polystyrene of low impact strength. As regards the previously known procedures, the metal splinters have been enclosed with a liquid plastic within a hollow mold, and then with the shell casing, by injection molding if desired.
This laborious procedure has been required so far because the known thermoplastics cannot be processed into densely filled molding compositions.